Magnetic Fields and Rotations of Protostars

Machida, Masahiro N.; Inutsuka, Shu‐ichiro; Matsumoto, Toshiro

doi:10.1086/521779

Cited by 155 publications

(309 citation statements)

References 37 publications

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“…The Ohmic diffusion coefficient is an increasing function of density and does not depend on the magnetic field. Roughly speaking, the Ohmic diffusion does not play a role when ρ 10 −13 g cm −3 (Machida, Inutsuka & Matsumoto 2007). Because the density of the first core is ρ 10 −13 g cm −3 , the magnetic flux piles up outside the first core.…”

Section: Structure Of the First Corementioning

confidence: 99%

Effects of Ohmic and ambipolar diffusion on formation and evolution of first cores, protostars, and circumstellar discs

Tsukamoto

Iwasaki

Okuzumi

et al. 2015

Mon. Not. R. Astron. Soc.

125

116

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We investigate the formation and evolution of a first core, protostar, and circumstellar disc with a three-dimensional non-ideal (including both Ohmic and ambipolar diffusion) radiation magnetohydrodynamics simulation. We found that the magnetic flux is largely removed by magnetic diffusion in the first core phase and that the plasma β of the centre of the first core becomes large, β > 10 4 . Thus, proper treatment of first core phase is crucial in investigating the formation of protostar and disc. On the other hand, in an ideal simulation, β ∼ 10 at the centre of the first core. The simulations with magnetic diffusion show that the circumstellar disc forms at almost the same time of protostar formation even with a relatively strong initial magnetic field (the value for the initial mass-to-flux ratio of the cloud core relative to the critical value is µ = 4). The disc has a radius of r ∼ 1 AU at the protostar formation epoch. We confirm that the disc is rotationally supported. We also show that the disc is massive (Q ∼ 1) and that gravitational instability may play an important role in the subsequent disc evolution.

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Section: Structure Of the First Corementioning

confidence: 99%

Effects of Ohmic and ambipolar diffusion on formation and evolution of first cores, protostars, and circumstellar discs

Tsukamoto

Iwasaki

Okuzumi

et al. 2015

Mon. Not. R. Astron. Soc.

125

116

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“…This alternative scenario is plausible if fragmentation occurs during the second collapse phase, a possibility which has been explored in the numerical simulations of Bonnell (1994) and Machida et al (2007). One of the conditions for this model to produce binary systems with typical separations ∼100−500 AU is that the initially very tight protobinary system must gain sufficient angular momentum by accretion (see e.g.…”

Section: Implications For the Formation Of Multiple Systemsmentioning

confidence: 99%

Toward understanding the formation of multiple systems

Maury¹,

André²,

Hennebelle

et al. 2010

A&A

157

230

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Context. The formation process of binary stars and multiple systems is poorly understood. The multiplicity rate of Class II premain-sequence stars and Class I protostars is well documented and known to be high (∼ 30% to 50% between ∼100 and 4000 AU). However, optical / near-infrared observations of Class I/Class II YSOs barely constrain the pristine properties of multiple systems, since dynamical evolution can quickly alter these properties during the protostellar phase. Aims. Here, we seek to determine the typical outcome of protostellar collapse and to constrain models of binary formation by core fragmentation during collapse, using high-resolution millimeter continuum imaging of very young (Class 0) protostars observed at the beginning of the main accretion phase. Methods. We carried out a pilot high-resolution study of 5 Class 0 objects, including 3 Taurus sources and 2 Perseus sources, using the most extended (A) configuration of the IRAM Plateau de Bure Interferometer (PdBI) at 1.3 mm. Our PdBI observations have a typical HPBW resolution ∼0.3 −0.5 and rms continuum sensitivity ∼0.1−1 mJy/beam, which allow us to probe the multiplicity of Class 0 protostars down to separations a ∼ 50 AU and circumstellar mass ratios q ∼ 0.07. Results. We detected all 5 primary Class 0 sources in the 1.3 mm dust continuum. A single component associated with the primary Class 0 object was detected in the case of the three Taurus sources, while robust evidence of secondary components was found toward the two Perseus sources: L1448-C and NGC1333-IR2A. We show that the secondary 1.3 mm continuum component detected ∼600 AU south-east of L1448-C, at a position angle close to that of the CO(2−1) jet axis traced by our data, is an outflow feature directly associated with the powerful jet driven by L1448-C. The secondary 1.3 mm continuum component detected ∼1900 AU southeast of NGC1333-IR2A may either be a genuine protostellar companion or trace the edge of an outflow cavity. Therefore, our PdBI observations revealed only wide (>1500 AU) protobinary systems and/or outflow-generated features. Conclusions. When combined with previous millimeter interferometric observations of Class 0 protostars, our pilot PdBI study tentatively suggests that the binary fraction in the ∼75−1000 AU range increases from the Class 0 to the Class I stage. It also seems to argue against purely hydrodynamic models of binary star formation. We briefly discuss possible alternative scenarios to reconcile the low multiplicity rate of Class 0 protostars on small scales with the higher binary fraction observed at later (e.g. Class I) evolutionary stages.

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“…In addition, the low-velocity outflow is driven by the outer edge of the rotating first core where the magnetic field is coupled with neutral gas ( On the other hand, the lifetime of the first core is as short as t ∼ < 100 yr when the angular momentum of the first core is sufficiently small (Masunaga & Inutsuka 2000;Saigo & Tomisaka 2006;Saigo et al 2008). In such a case, there is not enough time for dissipation of the magnetic field, and the magnetic field continues to be amplified without dissipation (Machida et al 2007). As a result, the amplification rate for the magnetic field depends on the first core lifetime or rotation rate.…”

Section: Cloud Collapse Before Protostar Formationmentioning

confidence: 99%

Different modes of star formation: gravitational collapse of magnetically subcritical cloud

Machida

Higuchi

Okuzumi

2017

Monthly Notices of the Royal Astronomical Society

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Star formation in magnetically subcritical clouds is investigated using a threedimensional non-ideal magneto-hydrodynamics simulation. Since rapid cloud collapse is suppressed until the magnetic flux is sufficiently removed from the initially magnetically subcritical cloud by ambipolar diffusion, it takes ∼ > 5-10 t ff to form a protostar, where t ff is the freefall timescale of the initial cloud. The angular momentum of the star forming cloud is efficiently transferred to the interstellar medium before the rapid collapse begins, and the collapsing cloud has a very low angular momentum. Unlike the magnetically supercritical case, no large-scale low-velocity outflow appears in such a collapsing cloud due to the short lifetime of the first core. Following protostar formation, a very weak highvelocity jet, which has a small momentum and might disappear at a later time, is driven near the protostar, while the circumstellar disc does not grow during the early mass accretion phase. The results show that the star formation process in magnetically subcritical clouds is qualitatively different from that in magnetically supercritical clouds.

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Magnetic Fields and Rotations of Protostars

Cited by 155 publications

References 37 publications

Effects of Ohmic and ambipolar diffusion on formation and evolution of first cores, protostars, and circumstellar discs

Effects of Ohmic and ambipolar diffusion on formation and evolution of first cores, protostars, and circumstellar discs

Toward understanding the formation of multiple systems

Different modes of star formation: gravitational collapse of magnetically subcritical cloud

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